{
  "codex": "The Physics Codex",
  "source_url": "https://thecodex.expert/physics/constants/",
  "schema_version": "1.0",
  "data_source": "NIST CODATA 2022 — physics.nist.gov/cuu/Constants",
  "codata_release_year": 2022,
  "last_updated": "2026-07-05",
  "next_review_trigger": "next CODATA release (expected 2026, published on ~2-year lag)",
  "constants": [
    {
      "name": "Speed of light in vacuum",
      "symbol": "c",
      "value": "299792458",
      "unit": "m s^-1",
      "uncertainty": "0 (exact, defining constant)",
      "notes": "Exact by definition since the 1983 SI redefinition of the metre."
    },
    {
      "name": "Planck constant",
      "symbol": "h",
      "value": "6.62607015e-34",
      "unit": "J Hz^-1",
      "uncertainty": "0 (exact, defining constant)",
      "notes": "Exact by definition since the 2019 SI redefinition."
    },
    {
      "name": "Reduced Planck constant",
      "symbol": "ħ (h-bar)",
      "value": "1.054571817e-34",
      "unit": "J s",
      "uncertainty": "0 (exact — derived from h)",
      "notes": "ħ = h / 2π."
    },
    {
      "name": "Newtonian constant of gravitation",
      "symbol": "G",
      "value": "6.67430e-11",
      "unit": "m^3 kg^-1 s^-2",
      "uncertainty": "0.00015e-11",
      "notes": "Least precisely known fundamental constant; relative uncertainty ~2.2e-5."
    },
    {
      "name": "Elementary charge",
      "symbol": "e",
      "value": "1.602176634e-19",
      "unit": "C",
      "uncertainty": "0 (exact, defining constant)",
      "notes": "Exact by definition since the 2019 SI redefinition."
    },
    {
      "name": "Boltzmann constant",
      "symbol": "k_B",
      "value": "1.380649e-23",
      "unit": "J K^-1",
      "uncertainty": "0 (exact, defining constant)",
      "notes": "Exact by definition since the 2019 SI redefinition."
    },
    {
      "name": "Avogadro constant",
      "symbol": "N_A",
      "value": "6.02214076e23",
      "unit": "mol^-1",
      "uncertainty": "0 (exact, defining constant)",
      "notes": "Exact by definition since the 2019 SI redefinition."
    },
    {
      "name": "Electron mass",
      "symbol": "m_e",
      "value": "9.1093837139e-31",
      "unit": "kg",
      "uncertainty": "0.0000000028e-31",
      "notes": "Relative standard uncertainty 3.1e-10."
    },
    {
      "name": "Proton mass",
      "symbol": "m_p",
      "value": "1.67262192595e-27",
      "unit": "kg",
      "uncertainty": "0.00000000052e-27",
      "notes": "Relative standard uncertainty 3.1e-10."
    },
    {
      "name": "Neutron mass",
      "symbol": "m_n",
      "value": "1.67492750056e-27",
      "unit": "kg",
      "uncertainty": "0.00000000085e-27",
      "notes": "Derived from deuteron binding energy measurements."
    },
    {
      "name": "Vacuum electric permittivity",
      "symbol": "ε₀",
      "value": "8.8541878188e-12",
      "unit": "F m^-1",
      "uncertainty": "0.0000000014e-12",
      "notes": "ε₀ = 1 / (μ₀c²). No longer exact after the 2019 SI redefinition."
    },
    {
      "name": "Vacuum magnetic permeability",
      "symbol": "μ₀",
      "value": "1.25663706127e-6",
      "unit": "N A^-2",
      "uncertainty": "0.00000000020e-6",
      "notes": "No longer exact after the 2019 SI redefinition; now tied to measured α."
    },
    {
      "name": "Fine-structure constant",
      "symbol": "α",
      "value": "7.2973525643e-3",
      "unit": "dimensionless",
      "uncertainty": "0.0000000011e-3",
      "notes": "Inverse fine-structure constant α⁻¹ = 137.035999177(21)."
    },
    {
      "name": "Rydberg constant",
      "symbol": "R∞",
      "value": "10973731.568157",
      "unit": "m^-1",
      "uncertainty": "0.000012",
      "notes": "Rydberg frequency cR∞ = 3.2898419602500(36)e15 Hz — one of the most precisely known constants."
    },
    {
      "name": "Stefan-Boltzmann constant",
      "symbol": "σ",
      "value": "5.670374419e-8",
      "unit": "W m^-2 K^-4",
      "uncertainty": "0 (exact — derived from k_B, h, c)",
      "notes": "σ = π²k_B⁴ / (60ħ³c²)."
    },
    {
      "name": "Faraday constant",
      "symbol": "F",
      "value": "96485.33212",
      "unit": "C mol^-1",
      "uncertainty": "0 (exact — derived from N_A and e)",
      "notes": "F = N_A × e."
    },
    {
      "name": "Molar gas constant",
      "symbol": "R",
      "value": "8.314462618",
      "unit": "J mol^-1 K^-1",
      "uncertainty": "0 (exact — derived from N_A and k_B)",
      "notes": "R = N_A × k_B."
    },
    {
      "name": "Bohr radius",
      "symbol": "a₀",
      "value": "5.29177210544e-11",
      "unit": "m",
      "uncertainty": "0.00000000082e-11",
      "notes": "a₀ = ħ / (α m_e c)."
    },
    {
      "name": "Electron volt",
      "symbol": "eV",
      "value": "1.602176634e-19",
      "unit": "J",
      "uncertainty": "0 (exact — derived from e)",
      "notes": "Energy gained by one elementary charge across a 1 V potential difference."
    },
    {
      "name": "Proton-electron mass ratio",
      "symbol": "m_p / m_e",
      "value": "1836.152673426",
      "unit": "dimensionless",
      "uncertainty": "0.000000032",
      "notes": "One of the most precisely determined mass ratios in physics."
    },
    {
      "name": "Magnetic flux quantum",
      "symbol": "Φ₀",
      "value": "2.067833848e-15",
      "unit": "Wb",
      "uncertainty": "0 (exact — derived from h and e)",
      "notes": "Φ₀ = h / (2e)."
    },
    {
      "name": "von Klitzing constant",
      "symbol": "R_K",
      "value": "25812.80745",
      "unit": "Ω",
      "uncertainty": "0 (exact — derived from h and e)",
      "notes": "R_K = h / e² = 2πħ / e². Basis of the quantum Hall resistance standard."
    },
    {
      "name": "Josephson constant",
      "symbol": "K_J",
      "value": "483597.8484e9",
      "unit": "Hz V^-1",
      "uncertainty": "0 (exact — derived from h and e)",
      "notes": "K_J = 2e / h. Basis of the Josephson voltage standard."
    }
  ]
}